Genetics and reverse epidemiology among patients on chronic hemodialysis

UCP2, a mitochondrial protein regulated at multiple levels

An ever-increasing number of studies highlight the role of uncoupling protein 2 (UCP2) in a broad range of physiological and pathological processes. The knowledge of the molecular mechanisms of UCP2 regulation is becoming fundamental in both the comprehension of UCP2-related physiological events and the identification of novel therapeutic strategies based on UCP2 modulation. The study of UCP2 regulation is a fast-moving field. Recently, several research groups have made a great effort to thoroughly understand the various molecular mechanisms at the basis of UCP2 regulation. In this review, we describe novel findings concerning events that can occur in a concerted manner at various levels: Ucp2 gene mutation (single nucleotide polymorphisms), UCP2 mRNA and protein expression (transcriptional, translational, and protein turn-over regulation), UCP2 proton conductance (ligands and post-transcriptional modifications), and nutritional and pharmacological regulation of UCP2.

MTHFR and HFE, but not preproghrelin and LBP, polymorphisms as risk factors for all-cause end-stage renal disease development

End-stage renal disease (ESRD) is a serious health problem worldwide. The high prevalence of cardiovascular diseases and chronic inflammation remains a major cause of morbidity and mortality in haemodialysed patients. Beside some external factors, genetic predisposition both to renal failure and poor prognosis has been assumed. We have collected a total of 1,014 haemodialysed patients and 2,559 unrelated healthy Caucasians. Single-nucleotide polymorphisms (SNPs) in genes for preproghrelin (GHRL), lipopolysaccharide-binding protein (LBP), HFE and MTHFR were genotyped. In the group of patients, significantly more carriers presented the MTHFR T667T (P = 0.002) and HFE Asp63Asp (P = 0.001) and Cys282Cys (P = 0.01) genotypes. The frequencies of individual SNPs within GHRL and LBP genes did not differ between the patients and controls. The trends in genotype frequencies did not differ between the subgroups of patients with different time on haemodialysis. Common variants in MTHFR and HFE could be a risk factor for all-cause ESRD development, but are not predictors for the survival on haemodialysis.

The -174G/C variant of IL6 as risk factor for mortality and technique failure in a large cohort of peritoneal dialysis patients

BACKGROUND

Functional variants in the IL6 gene, in particular the -174G/C polymorphism (rs1800795), affect the mortality risk in dialysis patients. Peritoneal dialysis (PD) patients harbouring the C allele of the -174G/C polymorphism of IL6 showed faster peritoneal transport. The aim of this study was to investigate this IL6 variant as risk factor for mortality and technique failure in a large cohort of Caucasian PD patients.

METHODS

A Dutch multicentre cohort of 398 incident PD patients (NECOSAD) was analysed. Survival analysis was performed for death and technique failure with a maximum follow-up of 5 years. A combined PD cohort from Amsterdam (Academic Medical Center, N = 71) and Brussels (Université catholique de Louvain Medical School, N = 102) was used for independent replication.

RESULTS

In NECOSAD, 105 patients died on dialysis [incidence rate 10.3/100 person-years (py)], and 138 patients experienced technique failure (16.2/100 py), with peritonitis as important cause. Patients with the C/C genotype had a 71% increased mortality risk compared to patients with the G/G genotype (95% confidence interval 0.98-2.98); this effect was mainly a long-term effect: a 2.7-fold increased mortality risk was found in patients having survived 2 years since the start on dialysis, and a 1.7-fold increased risk for the combined end point (mortality or technique failure). In the combined replication cohort, no increased risks were found in patients with the C/C genotype.

CONCLUSIONS

The C/C genotype of the -174G/C polymorphism was associated with an increased mortality risk in 398 Dutch incident PD patients. The existence of substantial differences between the two academic replication cohorts and the discovery cohort from NECOSAD and the limited power of these cohorts prevented an independent replication of the NECOSAD findings.

CRP polymorphisms and chronic kidney disease in the third national health and nutrition examination survey

BACKGROUND

CRP gene polymorphisms are associated with serum C-reactive protein concentrations and may play a role in chronic kidney disease (CKD) progression. We recently reported an association between the gene variant rs2808630 and CKD progression in African Americans with hypertensive kidney disease. This association has not been studied in other ethnic groups.

METHODS

We used data from 5955 participants from Phase 2 of The Third National Health and Nutrition Examination Survey (1991-1994) to study the association between CRP polymorphisms and CKD prevalence in a population-based sample. The primary outcome was CKD defined as estimated glomerular filtration rate (eGFR) <60 ml/min or the presence of albuminuria. Secondary outcomes were the presence of albuminuria (any degree) and continuous eGFR. Six single nucleotide polymorphisms (SNPs) from the CRP gene, rs2808630, rs1205, rs3093066, rs1417938, rs3093058, and rs1800947, were evaluated.

RESULTS

CRP rs2808630 AG compared to the referent AA genotype was associated with CKD in non-Hispanic blacks (n = 1649, 293 of whom had CKD) with an adjusted odds ratio (OR) of 3.09 (95% CI 1.65-5.8; p = 0.001). For the secondary outcomes, rs2808630 AG compared to the referent AA genotype was associated with albuminuria with an adjusted OR of 3.07 (95% CI 1.59-5.94; p = 0.002), however not with eGFR. There was no association between the SNPs and CKD, albuminuria or eGFR in non-Hispanic whites or Mexicans Americans.

CONCLUSIONS

In this cross-sectional study, the 3' flanking CRP gene variant rs2808630 was associated with CKD, mainly through its association with albuminuria in the non-Hispanic blacks. Despite not finding an association with eGFR, our results support our previous study demonstrating an association between CRP gene variant rs2808630 and CKD progression in a longitudinal cohort of African American with hypertensive kidney disease.

What is the meaning of homocysteine in patients on dialysis?

OBJECTIVE

To evaluate the determinants of total plasma homocysteine levels and their relations with nutritional parameters, inflammatory status, and traditional risk factors for cardiovascular disease in renal failure patients on dialysis treatment.

DESIGN

The study was conducted on 70 clinically stable patients, 50 of them on hemodialysis (70% men; 55.3 ± 14.5 years) and 20 on peritoneal dialysis (50% men; 62 ± 13.7 years). Patients were analyzed in terms of biochemical parameters (serum lipids, creatinine, homocysteine [Hcy], creatine-kinase [Ck], folic acid, and vitamin B(12)), anthropometric data, markers of inflammatory status (tumor necrosis factor-alpha, C-reactive protein, interleukin-6), and adapted subjective global assessment.

RESULTS

The total prevalence of hyperhomocysteinemia (>15 μmol/L) was 85.7%. Plasma folic acid and plasma vitamin B(12) were within the normal range. Multiple regression analysis (r(2) = 0.20) revealed that the determinants of total Hcy were type of dialysis, creatinine, Ck, folic acid, and total cholesterol. Hcy was positively correlated with albumin and creatinine and negatively correlated with total cholesterol, high density lipoprotein cholesterol, folic acid, and vitamin B(12).

CONCLUSIONS

The determinants of total Hcy in the study sample were type of dialysis, creatinine, Ck, folic acid, and total cholesterol. Evidently, the small sample size might have had an effect on the statistical analyses and further studies are needed. However, Hcy in patients on dialysis treatment may not have the same effect as observed in the general population. In this respect, the association between malnutrition and inflammation may be a confounding factor in the determination of the true relationship between Hcy, nutritional status, and cardiovascular risk factors in this group.

Malnutrition, inflammation, and lipids in a cohort of dialysis patients

BACKGROUND

This study aimed to determine if there is an association between lipid levels, serum albumin, and C-reactive protein (CRP) levels in patients on dialysis.

METHODS

Lipid profiles, albumin, and CRP levels were collected after a 12-hour fast from patients with end-stage renal disease (N = 105) who were on chronic hemodialysis. Patients were placed in an albumin group (>or= 3.8 g/dL) or a hypoalbumin group (< 3.8 g/dL), a high-risk CRP group (> 3 mg/dL) or a low-risk CRP group (<or= 3 mg/dL), and a low-risk group (low CRP and normal albumin) and high-risk group (high CRP and hypoalbumin). Lipid values included low-density lipoprotein (LDL), LDL particle number, LDL particle size, very-low-density lipoprotein (VLDL), large VLDL, high-density lipoprotein (HDL), large HDL, total cholesterol, lipoprotein A (Lp[a]), and triglycerides. All variables were measured using nuclear magnetic resonance spectroscopy.

RESULTS

Analysis of variance revealed significant differences in the hypoalbumin group, with LDL particle number being lower in this group. Analysis of variance revealed significant differences in LDL, VLDL, and LDL particle number, with lower levels in the high-risk CRP group. Analysis of variance also revealed significant differences in total cholesterol, VLDL, large VLDL, triglycerides, Lp(a), LDL, and LDL particle number when risk was combined with hypoalbumin and high CRP.

CONCLUSIONS

Our study found a counterintuitive effect in LDL and VLDL in patients with high CRP levels, in LDL particle number in patients with low albumin levels, and most variables when patients had both high CRP levels and low levels of albumin.

Chronic Kidney Disease and Inflammation: Role of +896A/G Pro-Inflammatory Polymorphism of TLR4 Gene and Δ32 Deletion of CCR5 Gene

Chronic inflammation seems implicated in the pathophysiology of chronic kidney diseases (CKD) and the development of its complications, such as cardiovascular diseases (CVD). Genes encoding inflammatory molecules are, hence, good candidates for CVD risk in haemodialysis patients (HD). We therefore evaluated whether +896A/G TLR4 polymorphism and CCR5A32 deletion are risk factors for CKD and CVD. We examined the two gene variants in 72 HD patients and in 125 controls from Sicily. No significant differences in the genotype distribution and allele frequencies of the two gene variants were observed between patients and controls. The same results were obtained by analysing the combined effect of the two proinflammatory (+896ATLR4 and wt CCR5) alleles. However, the high responder proinflammatory (+896A+TLR4/wt+CCR5) genotype seems to be a possible independent risk factor for CVD development in HD patients. Our results suggest that HD patients with a high responder pro-inflammatory genotype have an increase CVD risk.

Association of single-nucleotide polymorphisms in JAK3, STAT4, and STAT6 with new cardiovascular events in incident dialysis patients

BACKGROUND

Increasing evidence supports a role for cell-mediated immunity in the pathogenesis of cardiovascular disease. Single-nucleotide polymorphisms (SNPs) in JAK3, STAT4, and STAT6 of the Janus kinase-signal transducer and activator of transcription (Jak-Stat) signal transduction pathway were examined for association with time to new cardiovascular events in incident dialysis patients from the Choices for Healthy Outcomes in Caring for End-Stage Renal Disease Study.

STUDY DESIGN

Prospective cohort study.

SETTING & PARTICIPANTS

764 white (n = 518) and black (n = 246) participants from 79 dialysis centers.

PREDICTOR

SNPs in JAK3, STAT4, and STAT6 selected using a pairwise approach to identify a maximally informative set of tag SNPs for populations of European and African descent.

OUTCOMES & MEASUREMENTS

Cox proportional hazards models were used to estimate unadjusted and multivariable-adjusted hazard ratios (HRs) for incident cardiovascular disease events after dialysis therapy initiation associated with each race-specific SNP.

RESULTS

2 European tag SNPs (rs3212780 and rs3213409) in JAK3 were associated with new cardiovascular disease events in white patients with unadjusted HRs of 1.92 (P < 0.001) and 1.82 (P = 0.07), respectively. One dual-tag SNP (rs3212752) in JAK3 was associated with new cardiovascular events in white patients with an unadjusted HR of 2.09 (P < 0.001) and in black patients with an HR of 2.07 (P = 0.007). SNP rs3213409 codes for a valine to isoleucine change at amino acid 722, a potentially functional mutation. SNPs in STAT4 and STAT6 were not associated with cardiovascular events after the initiation of dialysis therapy.

LIMITATIONS

This study does not provide direct evidence for the mechanism of increased risk. Replication in independent cohorts is necessary.

CONCLUSIONS

Genetic polymorphisms in the Jak-Stat signaling pathway are associated with an increased risk of new cardiovascular events in incident dialysis patients.

Genetic predictors of renal failure

BACKGROUND

Both environmental and genetic factors contribute to the development and progression of chronic kidney disease. The completion of the human genome sequence and advances in genomic technology make possible identification of gene variants associated with renal failure.

OBJECTIVE

This review discusses the relevant genetic studies in chronic kidney disease, with particular emphasis on the most common causes of end stage renal failure, diabetic nephropathy and glomerulonephritis.

METHODS

Most of the studies presented were performed in recent years and employed association studies, both population-based and with candidate genes, as well as the genome-wide association and genome-wide scan approaches.

RESULTS/CONCLUSION

Increasing evidence supports an important role of genetic susceptibility in the development and progression of renal failure. Identification of disease genes will allow the identification of patients at high risk and the development of new strategies to prevent or delay the renal disease process.